Interpretive Summary: The regulation of cell division plays an important role in fiber initiation and development because about 25% of commercial cotton ovule epidermal cells stop division and develop to produce fibers. Cyclin-dependent kinases (CDKs) genes play an important role in the regulation of the cell division. Plant CDKAs not only control cell cycle progression, but also participate in cell proliferation and maintenance of cell division in differentiated tissues during development. The overall objectives of this research are to clone and characterize a fiber CDKA cDNA and its corresponding genomic sequences. The expression levels of the CDKA transcript and the CDKA protein were also studied in elongating cotton fibers from 5 to 20 DPA ovules and other tissues. The CDKA sequence data was used to develop single nucleotide polymorphism (SNP) markers specific for the CDKA gene(s) in cotton and the SNP markers was used with single primer extension technology to locate the CDKA gene to chromosome16 by deletion analysis. thus facilitate The mapping and investigation of candidate genes associated with fiber development will help in the genetic manipulation for improving cotton fiber.

Technical Abstract:
A cotton fiber cell normally originates and elongates as a single ovular epidermal cell. The cessation of fiber cell division and ensuing elongation imply that the cell cycle is differentially regulated in fiber cells. Cyclin-dependent kinases (CDKs) play a central role in the regulation of cell cycle, and thus could play important roles in cotton fiber initiation and/or development. A fiber GhCDKA cDNA encoding an A-type cyclin-dependent kinase have been cloned and characterized from an upland tetraploid cotton line, Gossypium hirsutum DES119. The encoded GhCDKA protein contains the conserved cyclin-binding, ATP-binding, and catalytic domains. Northern blot and RT-PCR analysis revealed that the GhCDKA transcript was high in 5-10 DPA fibers, moderate in 15 and 20 DPA fibers and roots, and low in flowers and leaves. Western blot revealed that GhCDKA protein levels increased from 5 to 15 DPA, peaked at 15 DPA, and decreased from 15 to 20 DPA. Oligodeoxynucleotides designed from the conserved GhCDKA sequence were used as primers to amplify and sequence genomic DNAs from three diverse cotton lines of TM-1 (G. hirsutum), 3-79 (G. barbadense) and CMD11 (G. tomentosum). Several single-nucleotide polymorphisms (SNP), about one per 100 bases, were detected in the 5’-flanking region of the CDKA gene among the three lines. A primer specific to one of the SNP was used with single primer extension technology to detect polymorphism at single homologous locus between TM-1 and 3-79 for the CDKA gene, which we subsequently delimited the CDKA locus to chromosome 16 by deletion analysis with a series of hypoaneuploid interspecific hybrids.